| Background:Dental ceramics is admirable in biological properties and corrosion resistence and acid-base resistance properties.It also has a prominentaesthetic performance,which is highly praised by doctors and patients,but compared with alloy and resin and other polymer inlay material,it has low bending strength and fracture toughness.Its most fatal weaknesses are brittleness and fragility.Its inherent brittleness restricts further application and development.Changing its brittleness and improvingfracture toughness has always been thehot spot of the ceramics research at home and abroad.In 2015,the United States 3M company released the world’s first CAD/CAM Restorative nano composite ceramic-LavaTM Ultimate,Because of the 80wt%(65vol%)pre-polymerization of nano-ceramic particles,LavaTM Ultimate ceramics are considered to be a new type of dental restorative materials.Fracture toughness refers to the ability of the material to resist crack propagation,which is the only index to characterize the brittleness of the material and the most important mechanical performance index.The lower fracture toughness values reduce the reliability of the clinical application of the ceramic restorations,because the fracture toughness values reflect the critical stress intensity levels due to an irreversible damage caused by a critical defect.Therefore,each new dental ceramic repair material should be tested before being widely used in the clinic,and test its fracture toughness value.Objective:In this study,we used LavaTM Ultimate and Ceramage,IPS e.max Press to repair the hardness and fracture toughness,Ceramage and IPS e.max Press are two kinds of commonly used inlay repair materials.It is necessary to provide a theoretical basis for the clinical application of the new generation of inlay repair materials for LavaTM Ultimate.Materials and methods:1.Specimen making and grouping:According to different materials,two for each group,a total of 6 groups: Lava TM Ultimate group(Cylindrical group,rectangular group),Ceramage group(Cylindrical group,rectangular group),IPS e.max Press group(Cylindrical group,rectangular group).According to the method recommended by the manufacture,processing plant completed the production of three kinds of materials,cylindrical specimens were made with thickness of 2.0mm,diameter of15.0mm and rectangular specimens were made with length of 15.0mm,width of1.25 mm,height of 2.5mm.6 pieces of each group.2.Experimental measurement:Indentation hardness test: Three sets of cylindrical specimens were fabricated on the surface of the 18 samples,making use of the digital display Vivtorinox hardness tester.The test piece was placed on the opposite side of the surface with a 136 degree positive four pyramid shaped diamond indenter,the load was 98 N,and the pressure holding time was 15 seconds,each specimen was measured at 5 points in different locations.The two diagonal lengths of the indentation on the surface of the test specimen were observed under the inverted metallographic microscope,and the length of each of the 2 diagonal lines was measured,Calculate their average.The hardness of each specimen was calculated according to the formula.Three point bending test: The three groups of rectangular specimens were first cut by linear cutting in the first place,then the three point bending test was performed on a microcomputer controlled electronic universal testing machine,recorded the maximum load value of each specimen when it broke.The fracture toughness values of each specimen were calculated according to the formula.3.Data analyzed: The data obtained from this experiment was based on SPSS Statistics 17 statistical software.First of all,the three sets of test specimens were tested by non parametric-one sample K-S test,and the results show that the three sets of test data were in line with the normal distribution,then,the discard of suspicious data was analyzed,and the hardness and fracture toughness values of three kinds of inlay restorations were analyzed by one-way ANOVA.If there was a significantdifference between the 3 groups,the 3 groups were compared by Tukey HSD test for the comparison of the 22.Test level alpha =0.05,p<0.05 was found to be statistically significant.Result:1.The hardness values of three kinds of inlay restorations were statistically analyzed,the results showed that there was a significant difference in the hardness values of LavaTM Ultimate group,Ceramage group,IPS e.max Press group(p<0.05).2.The fracture toughness values of three kinds of inlay restorations were statistically analyzed,the results showed that there was a significant difference in the fracture toughness values of LavaTM Ultimate group,Ceramage group,IPS e.max Press group(p<0.05).3.Tukey HSD test was used to compare the mean values of hardness and fracture toughness values between the 3 groups in the 22 groups.The results showed that there was a significant difference(p<0.05)between the hardness values of 22,and the fracture toughness value of the comparison was also significant difference(p<0.05).Conclusion:1.IPS e.max Press group had the highest hardness value,followed by group LavaTM Ultimate,Ceramage group had the lowest hardness;2.Fracture toughness of Ceramage group was the largest,followed by group LavaTM Ultimate,the fracture toughness of IPS e.max Press group was the lowest. |
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